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Plate Tectonics/2017 Transcript
Transcript Text reads: The Mysteries of Life with Tim and Moby Tim and Moby are seated beside each other in a two-person submarine, deep beneath the surface of an ocean. The submarine has bright headlights and a clear dome that protects them from the pressure of the water around them. TIM: Are you sure this thing is rated for this depth? MOBY: Beep. Moby opens an AirMall catalog and shows Tim an advertisement for the submarine they are in. Text in the ad reads: Now on sale. Three percent discount. Get your own mini-submarine. Buy it today! TIM: You bought it from an AirMall catalog? Oh, great. Tim reads from a typed letter. TIM: Dear Tim and Moby, when I look at a map; it seems like some continents fit together perfectly. Are my eyes playing tricks on me? From, Georgia. You're not seeing things, Georgia. Some continents look exactly like puzzle pieces that snap together. An animated map shows South America and Africa pressed together as Tim describes. TIM: Early mapmakers suspected that they were all once connected. MOBY: Beep. An image shows a world map with a single, huge continent. TIM: In the early twentieth century, a scientist named Alfred Wegener called this supercontinent Pangaea. An image shows a portrait of Alfred Wegener. TIM: He thought different chunks of it broke off and slowly moved apart. The animated world map shows Pangaea breaking into several pieces which drift apart from one another. A digital stopwatch times the process. Text beneath the stopwatch reads: Millions of years ago. TIM: Over millions of years, they formed the continents we know today. The continents assume the shapes we know today. The stopwatch reaches "zero." MOBY: Beep. TIM: Wegener couldn't explain why Pangaea split up, or how. Tim and Moby steer their submarine into an underwater grotto. TIM: But there was some evidence to support his idea. Fossils from similar plants and animals had been found oceans apart. An image shows South America and Africa. Illustrations indicate the presence of identical fossils on both continents. TIM: The age and type of rock layers matched up, too. Images show identical-looking rock layers on both continents. TIM: Wegener's theory of continental drift provided an explanation. Wegner stands on a theater stage, giving a lecture. He holds a sheet of paper and gestures at an easel displaying the images Tim has just described. TIM: But his ideas weren't taken seriously until long after he died. A tomato is thrown at Wegener from the audience. It hits the image on the easel and slides toward the floor. MOBY: Beep. TIM: In the 1950s, scientists began mapping the Mid-Atlantic Ridge. It's a mountain range running ten thousand miles along the ocean floor. An animation shows the Mid-Atlantic Ridge. It is an underwater mountain range running midway down the Atlantic Ocean, between the Americas on the left and Europe and Africa on the right. TIM: Tests revealed that the farther you got from the ridge, the older the seafloor was. An animated chart illustrates what Tim describes. The farthest seafloor shown formed 2.5 million years ago. TIM: So, a geologist named Harry Hess proposed a revolutionary idea. An animation shows Harry Hess with a light bulb over his head. He holds up a finger to indicate that he has an idea. MOBY: Beep. TIM: New seafloor was forming at the ridge and spreading outward to make room for more. In other words, the surface of the planet was moving. Hess called this process seafloor spreading. It seemed to indicate that rock was being forced up from inside the planet. An animation shows the seafloor moving up and away from the ridge as Tim describes. TIM: Nowadays, we can see this rock formation in action. Tim and Moby take their submarine near the bottom of the ocean. Lava oozes slowly from the rock below them. TIM: Wegener had guessed something like this, but he had no way to prove it at the time. MOBY: Beep. TIM: As he suspected, there's a lot going on beneath the earth's surface. Up here, everything seems pretty cool and stable. But miles below our feet, it's a raging inferno. An animation shows a cross section of Earth, with temperatures becoming gradually hotter between the planet's surface and its center. MOBY: Beep. TIM: The deeper you go, the hotter it gets. Earth's center, or core, is as scorching as the surface of the Sun. All that energy wants to escape, like steam inside a boiling kettle. It pushes outward, putting immense pressure on the middle section, the mantle. The animation shows arrows pushing outward from the core to the mantle, illustrating the process Tim describes. TIM: Standing in its way is the lithosphere, a rigid layer of solid rock. The animation shows the lithosphere which surrounds the mantle. MOBY: Beep. TIM: Well, the lithosphere isn't like a smooth shell. It's cracked into pieces, each one a different size, shape, and thickness. An animation shows the earth's surface cracking into irregular pieces. TIM: We call those pieces plates. An animated world map uses dotted lines to show the boundaries of the plates. MOBY: Beep. TIM: Yup, the Mid-Atlantic Ridge is the border between several plates. They're being dragged apart by forces from deep inside the planet. One dotted line becomes illuminated, highlighting the location of the Mid-Atlantic Range. TIM: You can think of it like a pot of soup. The earth's core is the burner, and the mantle is the boiling soup. As the soup near the burner heats up, it becomes less dense and rises. When it gets to the top, it cools off and sinks down toward the heat. An animation shows a pot of soup bubbling on a stove. A cutaway side-view of the pot shows the soup rising from the bottom center of the pot, reaching the top, and then moving back down the sides of the pot to the bottom. TIM: In physics, those are called convection currents. A similar process is driving the mantle, and it's taking the plates along for the ride. That movement is called plate tectonics. An animation shows a cutaway side-view of lava beneath the bottom of the ocean. It is moving upward in a similar manner to the soup in the center of the pot. As the lava rises to the ocean's bottom it forms new land, forcing the plates apart. MOBY: Beep. TIM: It's the engine driving the constant transformation of our planet's surface. Plates have been bouncing off each other for eons. The oceans have expanded and contracted. An animated map of the world illustrates the process Tim describes. TIM: Landmasses have smashed into each other and broken apart. An animation shows landmasses involved in volcanic activity. MOBY: Beep. TIM: The plates move about as fast as your fingernails grow, so we don't see the ground sliding around under our feet. But we do sometimes feel it. MOBY: Beep. TIM: Yep, I'm talking about earthquakes. Seismic activity is greatest along plate borders. An animation shows a suburban neighborhood being shaken by an earthquake. TIM: At convergent boundaries, where two plates collide; at divergent boundaries, where they pull apart; and at transform boundaries, where they slide past each other. Animations illustrate the three different types of plate boundaries as Tim describes them. TIM: At all three boundaries, there's enormous pressure on the earth's crust. That's the topmost layer of the lithosphere. An animation shows lava moving beneath the earth's crust. TIM: The pressure can build up for years. The longer it takes to release, the bigger the earthquake. The animation shows the top of the lithosphere, or the earth’s crust. A crack forms on a highway, splitting it in two down the center. MOBY: Beep. TIM: Yep, and plate movement drives volcanic activity, too. Tim and Moby guide their submarine to a shipwreck at the ocean's bottom. TIM: At divergent boundaries like the Mid-Atlantic Ridge, there's a gap in the lithosphere. So, magma, molten rock from the mantle, is constantly pushing up along the boundaries. These are the most volcanically active places on Earth. Animations illustrate the volcanically active gap at the Mid-Atlantic Ridge. Tim and Moby slowly approach the gap with their submarine. TIM: Volcanoes are also common at boundaries called subduction zones. That's when a dense ocean plate converges with a lighter continental plate. The heavier plate gets pushed below, down into the mantle. Some of it melts, and the magma erupts farther inland. An animation showing ocean, land, and underground activity illustrates the process Tim describes. TIM: The Ring of Fire is a massive chain of these volcanoes. Dense sedimentary rock making up the Pacific seafloor is subducted, transformed into metamorphic rock through pressure and heat, and then recycled as igneous rock through volcanic eruptions. An animation of a world map illustrates the Ring of Fire, a chain of volcanoes all along the Pacific coasts of North America, South America, and Asia. TIM: In other words, plate tectonics drives the rock cycle, the constant process of transformation and renewal of the earth's crust. An animation illustrates the three phases of the rock cycle, showing the formation of sedimentary, metamorphic, and igneous rock as Tim described. TIM: It also creates our most prominent geologic features, mountain ranges. MOBY: Beep. TIM: That happens when two continental plates converge. Since they're both about the same density, neither one subducts. Instead, it's like a slow-motion car crash. The plates buckle and warp. The land pushes up into jagged peaks. An animation uses arrows to illustrate the pushing movements Tim describes. TIM: The Himalayas are still growing from a plate collision that began half a billion years ago. An animation of Asia shows the collision between the Eurasian Plate and the Indian Plate that formed the Himalayan mountain range. MOBY: Beep. TIM: Yeah, Alfred Wegner's theory has come a long way in a hundred years. He was practically laughed out of the scientific community for his ideas. But today, plate tectonics is the unifying theory that ties together the entire field of geology. Side by side images show Wegner with a tomato thrown at him, and a present-day museum wing named after him displaying different kinds of rocks. MOBY: Beep. Tim and Moby shut off their submarine's engine, and the submarine settles to the bottom of the ocean floor. The ocean is very still and quiet. TIM: What do you mean, out of juice? We're stuck here? A tentacle touches the outer dome of their submarine. Tim yells, startled. TIM: Now what? An octopus watches them from outside the submarine. Moby puts on goggles and a snorkel. He hands a second snorkel to Tim. MOBY: Beep. TIM: Oh, thank you. 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